Typical commercially available tire pressure monitoring system units are mounted to the inside of a tire in a position from which the air pressure within the tire cavity may be measured. Data representing pressure within the tire is then communicated by a transmitted signal to a reader external to the tire. For example, certain available units integrate a pressure sensing module with the valve stem of a tire. Electronics within the sensor unit measure the air pressure at the valve stem and transmit an appropriate signal to an external receiver. The receiver may be proximally located to the sensor unit or in a remote location such as the passenger compartment.
While working well, such systems are not useful in meeting the industry's needs in certain applications. For example, in some applications, such as in NASCAR race tires, there is a need for a tire pressure-measuring device that may be used conveniently in a two tire system by officials to check start inflation pressure. A rim-mounted tire pressure monitoring system has been proposed and is the subject of co-pending U.S. patent application Ser. No. 11/641,333 filed Dec. 19, 2006, incorporated herein by reference.
In a rim mounted system, a housing typically molded of plastics material is employed to house sensor and communication electronics. The housing has an internal pressure chamber; a pressure sensing device within the housing pressure chamber, and a portal communicating through the wheel rim between the internal housing pressure chamber and a tire air cavity. The TPMS housing unit is mounted to a rim ledge with a bolt. The bolt has a hole drilled therethrough to allow communication of the inflation pressure within the tire to the pressure chamber within the TPMS housing. The bolt threads into a threaded insert nut that is molded into the plastic TPMS housing. An appropriate seal is used between the insert nut and the rim. In other systems, a pipe is attached to a portal within the rim through which pressure is communicated with the housing pressure chamber. The pipe routes along an outer rim surface to a different rim location where the pipe attaches to a second portal through the rim.
While working well, a rim mounted TPMS housing is exposed to potentially damaging external forces. It is possible for the TPMS housing to become damaged and even disconnected from the rim ledge mounting surface under certain situations. In such an event, the air within the tire will leak rapidly out of the hole in the bolt, potentially resulting in loss of control of the vehicle. In a dual portal system utilizing a pipe extending between two passageways in the rim, damage to the pipe or the TPMS housing can result in the exposure of a passageway and resultant rapid loss of air from a tire. In applications where the vehicle is driven at high speed, such as NASCAR racing, it is even more important to prevent rapid pressure loss in a tire that can negatively impact the driver's control of the vehicle.
Accordingly, a need exists in rim-mounted TPMS systems for a means to avoid rapid deflation of a tire through a rim portal in the event that the portal becomes exposed. Exposure of a portal may occur where an external TPMS housing becomes damaged or detached from the rim or where ancillary hardware such as a connector pipe detaches from a portal in a wheel rim. Ideally, the solution to the industry's needs would be capable of giving the driver a warning early enough to allow the driver to take corrective action before tire inflation crosses over a critical safety threshold.